The invention relates to a method for producing an inkjet printhead element and an inkjet printhead element produced using said method.
Inkjet printheads generally comprise two members, the thinfilm die and the metal orifice plate. These members are generally manufactured separately and are subsequently brought together to form a unified inkjet printhead element. Traditionally, the attachment of the thinfilm die to the metal orifice place has been accomplished via an ink barrier layer on the thinfilm die. In the attaching process, dollops of glue are dispensed to temporarily tack the orifice plate in position before the thinfilm die and the orifice plate are permanently secured to one another by performing a so-called xe2x80x9cstake and bakexe2x80x9d procedure.
The process of attaching the thinfilm die to the orifice plate using dispensed glue has, however, been fraught with problems. It is for example very difficult to control the size and the position of the glue which is dispensed. Another grave problem which occurs is that the orifice plate, temporarily tacked in place on the liquid glue, slides laterally on the layer of liquid glue relative to the thinfilm die prior to being permanently affixed in the staking process. This shifting leads to improper alignment of the orifice plate on the thinfilm die in the staking process.
Generally, the inability to control the size of the dispensed glue dollops leads to a lifting of the corner of the orifice plate from the thinfilm die if too much glue is used, or complete separation of the orifice plate from the thinfilm die in the case that too little glue is used. Furthermore, the inability to control the positioning of the dispensed glue leads to the existence of glue in unintended locations on the thinfilm die and/or on the orifice plate, a situation leading to problematic smearing of the glue. This either worsens print quality or, in extreme cases, leads to rejection of the printhead, thereby increasing production costs.
U.S. Pat. No. 6,054,011 discloses an orifice plate with a layer of metal, for example gold, bonded thereto and an ink barrier layer. An adhesion promoter glue is provided between the ink barrier layer and a metal oxide layer which itself is applied to the metal layer which is bonded to the orifice plate. The orifice plate is therefore held to the ink barrier layer via the direct adhesion contact between the metal oxide layer and the adhesion promoter glue. According to this document, the orifice plate and the ink barrier layer are assembled by compressing the orifice plate, coated as indicated above, to the ink barrier with the polymeric adhesion promoter there between at a pressure of about 150 psi (105,555 kg/m2) at a temperature of about 200xc2x0 C. for about 10 minutes. Following compression and heating as above, the ink barrier layer-orifice plate assembly is heated (with the adhesion promoter glue there between) at a temperature of about 220xc2x0 C. for about 30 minutes.
A problem with existing glue-based processes is that when the orifice plate, following temporary tacking to the thinfilm die, is subjected to the stake process at 150xc2x0 C., the glue used for temporarily tacking melts and causes misalignment of the orifice plate on the thinfilm die. This can lead to smearing of glue if the amount and/or position of the glue is not correct.
It is therefore a goal of the present invention to produce an inkjet printhead element in which in which the final alignment of the orifice plate on the thinfilm die is improved.
This goal is met by providing a method for producing an inkjet printhead element comprising the features recited according to the independent claim.
A method for producing an inkjet printhead element comprises providing a thinfilm die and a barrier layer thereon, wherein the barrier layer comprises a thermoplastic component and a thermoset component. The barrier layer is heated such that the barrier layer becomes tacky. The orifice plate is aligned to the barrier layer and is brought into contact with the barrier layer. Here, the orifice plate is held in place on the barrier layer by the tackiness of the barrier layer. Finally, the assembly of the thinfilm die, the barrier layer and the orifice plate is subjected to a stake and bake process to attach the orifice plate permanently to the barrier layer and, hence, to the thinfilm die.
A major advantage of the inventive method as recited above is that no glue is used in the barrier layer for temporarily tacking the orifice plate to the thinfilm die. The barrier layer is heated just enough to reach the glass transition temperature of its thermoplastic component. The thermoplastic component of the barrier layer becomes highly amorphous such that the entire surface of the barrier layer becomes sticky to the touch. This stickiness will subsequently hold the orifice plate in place when the orifice plate is placed on top of the barrier layer.
Adhesion in the inventive method recited above takes place directly between the orifice plate and the barrier layer, i.e. no glue is needed, the temporary adhesion of the orifice plate on the barrier layer prior to curing instead depending on the tackiness of the barrier layer upon reaching its glass transition temperature Tg. Since the orifice plate is directly contacted lightly to the already tacky barrier layer instead of using glue to temporarily tack the orifice plate, the danger of glue being squeezed out from in between the orifice plate and the barrier layer into undesired regions is essentially eliminated. This leads to a lower reject ratio, thereby streamlining and economizing the entire production process.
The fact that the orifice plate is directly tacked to the barrier layer offers greater resistance to a shifting of the orifice plate on the barrier layer prior to staking and/or curing the orifice plate on the barrier layer. This means that proper alignment of the orifice plate on the barrier layer can be controlled to be more precise and more reproducible in the absence of the shifting of the orifice plate and the barrier layer relative to one another.
The method according to the invention as recited above comprises two heating phases.
The first of these two heating phases is intended to prepare the barrier layer for the subsequent contacting of the orifice plate, and therefore takes place prior to such contacting. During this first of two heating phases, the barrier layer is heated to within approximately 2% of the glass transition temperature of its thermoplastic component. This first heating phase is therefore not intended to liquefy the entire barrier layer but rather only to render one of the barrier layer""s components, the thermoplastic component, highly amorphous so that the entire surface of the barrier layer becomes tacky to the touch. Since it is not intended that the barrier layer be melted prior to contacting the orifice plate on the barrier layer, the heating conditions to which the barrier is subjected in this first heating phase can and, advantageously, should be kept gentle. Especially characteristic of the gentleness of this first heating phase is the fact that the heating of the barrier layer to only its approximate glass transition temperature can be accomplished very quickly. Once the approximate glass temperature of the thermoplastic component of the barrier layer is reached, an orifice plate can be contacted with the (now tacky) barrier layer.
Between the two heating phases, the orifice plate is first aligned with the barrier layer with which it is to be brought in contact and is then brought in contact with the (tacky) barrier layer. The danger of glue being displaced from in between the barrier layer and the orifice plate during the process of contacting the orifice plate to the barrier layer is essentially ruled out by two characteristic features of the invention:
a) The barrier layer is merely tacky and is not in liquid form, so that it cannot flow into unintended regions, and
b) The contacting of the orifice plate to the barrier layer is itself accomplished very gently, preferably by merely touching the orifice plate to the barrier layer; the tackiness of the barrier layer engendered during the first heating phase as described above is sufficient to hold the incoming orifice plate securely, thereby obviating any active compression of the orifice plate onto the barrier layer. It is such active compression which is in part responsible for the undesired displacement of adhesion material in other related methods in the prior art.
The second heating phase of the method according to the invention is carried out following the contacting of the orifice plate to the barrier layer by a stake process at a pressure of 150 psi and a temperature of 200xc2x0 C. and then a bake process of 200xc2x0 C. for 20-30 min to set the thermoset component of the barrier layer. During this second heating phase, the duration of which will depend on the time necessary for the particular thermoset component used in the barrier layer to cure, the orifice plate therefore becomes permanently attached to the thinfilm die via the interposed barrier layer.